Process for electroplating polyoxymethylene

ABSTRACT

An improved process for electroplating polyoxymethylene is provided wherein shaped articles of polyoxymethylene are treated with pyridine preferably by immersion techniques prior to subjecting the shaped article to surface treatment with an acid etching agent.

United States Patent [191 Deyrup [4 1 Sept. 16, 1975 PROCESS FORELECTROPLATING 1 POLYOXYMETHYLENE [75] Inventor: Edward Johnson Deyrup,Northeast,

[73] Assignee: E. I. Du Pont de Nemours and 1 Company, Wilmington, Del.

22 Filed: Feb. 19, 1974 21 App1. No.: 443,204

[52] US. Cl. 204/30;' 29/195; 117/47 A;

204/20; 204/32 R; 204/38 E [51] Int. Cl. C25D 5/56 [58] Field of Search204/20, 30, 38 E;

[56] 1 References Cited UNITED STATES PATENTS 3,414,427 12/1968 Levy117/47 Primary Examiner-John H. Mack Assistant Examiner-Aaron Weisstuch[5 7] ABSTRACT An improved process for electroplating polyoxymeth' yleneis provided wherein shaped articles of polyoxymethylene are treated withpyridine preferably by immersion techniques prior to subjecting theshaped article to surface treatment with an acid etching agent.

2 Claims, No Drawings PROCESS FOR ELECTROPLATING POLYOXYMETHYLENE FIELDOF THE INVENTION The present invention relates to a process forelectroplating shaped structures of polyacetal polymeric material and,more particularly, is directed to a novel improved process forelectroplating articles of polyoxymethylene.

BACKGROUND OF THE INVENTION Processes and 'methods for electroplatingshaped structures or objects of polyacetal resins such aspolyoxymethylene are known. For example, US. Pat. No.

3,5 54,880 discloses a process for electroplating an article ofpolyoxymethylene which comprises first subjecting the article to asurface preparation treatment by immersing the article in an acid agentsuch as orthophosphoric acid thereby to etch the surface of the article.The acid-etched article is thereafter treated as by an immersiontechnique with a basic solution such as sodium hydroxide. The thustreated article is then subjected to the conventional electroplatingtechnique which entails the sequential steps of treating the articlewith sensitizing agents and activating agents followed by depositing anelectroless plating of, for example, copper on the article andthereafter electroplating the article in a conventional electroplatingbath. A drawback and continuing problem encountered heretofore asregards the electroplating of polyoxymethylene articles has been theinability to obtain plated articles wherein the metal plating is firmlybonded to the sur face of the plastic article. Oftentimes, the metalcoating on the plastic object will exhibit undesirable blistering whenthe plated plastic object is subjected to a thermal cycle of heating andcooling, and the plastic objects often exhibit undesirable surfacecracks which are be lieved to be induced by the acid etchant. Theprincipal object of the present invention is to provide an improvedprocess for electroplating shaped articles and objects of polyacetalresins such as polyoxymethylene that are characterized by more firmlyadhered metal coatings and substantially free of the above-mentioneddrawbacks.

THE INVENTION According to the present invention there is provided in aprocess for electroplating a shaped article of polyoxymethylene by thesequential steps of etching the surface of said article with an acidetching agent such as orthophosphoric acid, neutralizing the etchedsurface of said article with a basic solution such as sodium hydroxide,treating said article with a noble metal catalyst such as palladium,depositing by electroless plating a metal coating such as nickel on saidarticle, and depositing by electroplating a metal coating such asnickel, copper or chrome on said electroless plated article, theimprovement which comprises treating said article with pyridine beforeetching the surface of said article.

DETAILED DESCRIPTION The nature and advantages of the present inventionwill be more clearly understood by the following more detaileddescription thereof.

The salient feature of the present invention is the discovery thatsubjecting polyoxymethylene shaped articles to a treatment with pyridineprior to the conventional pre-treatment with acid etchants and catalysts(for electroless deposition) prior to the electroless plating and theelectroplating thereof results in superior plated polyoxymethyleneshaped articles characterized by a unique surface topography afteretching and a more uniformly etched surface, fewer acid-etchant inducedsurface cracks, and unexpected and surprising adhesion of the metalcoating characterized by superior resistance to blistering of the metalcoating.

The improved process of the present invention may be practiced bytreating the shaped articles of polyoxymethylene with pyridine. This ispreferably done by immersing the polyoxymethylene article in thepyridine. The pyridine utilized for the treatment may be a solutionentirely of pyridene or an aqueous solution of pyridine containing up toabout 7.5 percent by volume of water.

After the pyridine treatment, the polyoxymethylene article is subjectedto a preplate process and an electroplating process similar to thatdescribed in the aforementioned U.S. Pat. No. 3,554,880.

The principle and practice of the present invention will now beillustrated by the following Examples which are exemplary only and it isnot intended that the invention be limited thereto since modificationsin technique and operation will be apparent to anyone skilled in theart. All parts and percentages specified in the Examples are by volumeunless otherwise specified.

EXAMPLE Polyoxymethylene resins containing 0.75 percent by weight ofnylon stabilizer and 0.125 percent by weight antioxidant (GAO-5 ,2,2'-methylene-bis-( 4-methyl-6-tbutyl) phenol and having the numberaverage molecu lar weight indicated in Table 1 below were molded byconventional molding techniques at the temperature also indicated inTable 1 into plaques having a planar dimension of 3 inches by 6 inchesand a thickness of one-eighth inch.

The plaque samples were immersed for 2 minutes into an alkaline cleanersolution comprising 6 oz. of Metex S1651 (MacDermid, Inc.., Waterbury,Connecticut) per gallon of distilled water maintained at 84C. andthereafter rinsed for 2 minutes with water at room temperature.

The cleaned plaque samples were next immersed for 5 minutes in asolution of 30% pyridine and distilled water maintained at 60C.,followed by a l minute rinse with water at room temperature.

The pyridine-treated plaque samples were next immersed for two minutesin a solution of distilled water containing 83% by volume of 85% byweight orthophosphoric acid maintained at 70C., followed by a one minuterinse with water at room temperature.

The acid etched plaque samples were next immersed for 6 minutes in adistilled water solution containing 12% by weight sodium hydroxidemaintained at 104C.

The base-neutralized plaque samples were next immersed for 10 minutes ina distilled water solution con taining 1% by volume of acetic acidmaintained at C.

The surface treated polyoxymethylene plaque samples were next subjectedto electroless nickel plating in the following manner: (1) the plaqueswere first immersed for 2 minutes in a preactivator bath (maintained atroom temperature) consisting of a solution of distilled water containing1% by volume of MACuplex Preactivator PA-3 (MacDermid, Dermid, Inc.,Waterbury, Connecticut), followed by a one minute rinse water at roomtemperature, (2) the plaques were next immersed for 2 minutes in apalladium activator bath (maintained at room temperature) consisting ofa solution of distilled water containing by volume of MACuplex ActivatorD-34 (MacDermid, Inc., Waterbury, Connecticut) and 20% by volume of HCI,followed by a 1 minute rinse with water at room tempera- 1O ture, (3)the plaques were next immersed for one minute in an accelerator bath(maintained at 50C.) consisting of an aqueous solution of distilledwater containing 5% by volume of MACuplex D-45 Accelerator (MacDermid,Inc., Waterbury, Connecticut), followed by a one minute rinse with waterat room temperature, (4) the plaques were next electroless plated byimmersing the plaques for 10 minutes into a commercially availableelectroless nickel bath (maintained at 30C.)

consisting of a solution of distilled water containing about 10% byvolume of MACuplex J-6O Electroless Ni concentrate (MacDermid, Ine.,Waterbury, Connecticut) and about 3% by volume of MACuplex ElectrolessNi Reducer J-6l (MacDermid, Inc., Waterbury, Con- The electroplatedplaque samples were next repeatedly subjected to the following thermalcycle: l heating to 180F. and holding at that temperature for 1 hour,(2) cooling to room temperature and holding at room temperature for 15minutes, (3) cooling to -F. and holding at that temperature for 1 hour,and

(4) heating to room temperature and holding at that temperature 15minutes, and evaluated for blistering after each cycle. The results arereported in Table l below.

For comparative purposes, the foregoing procedure was repeated exceptthat the polyoxymethylene plaque samples were not subjected to thepyridine treatment. The results also are reported in Table 1 below.

In both cases described above, polyoxymethylene plaque samples wereevaluated for surface cracks; these samples were prepared in accordancewith the procedure described above except that the electroless nickelplating was conducted for 5 minutes instead of' 10 minutes, in order toobtain a thinner layer of electroless nickel to facilitate evaluationfor surface cracks. The summation of the length of the cracks induced onthe surface of the plaque samples also is presented in Table 1 belowunder the column ZCL.

TABLE 1 Surface Area Number Average Molding Pyridine Number of ThermalBlistered After ECL, Sample Molecular Weight Temperature, F. TreatedCycles to Blister l5 Cycles, mm

1 33,000 185 No I I .5 372 2 33,000 I85 Yes 15 0 I66 3 33,000 2I() No I0.2 295 4 33,000 2 I 0 Yes I 5 0 0 5 39,000 I85 No I 50 lst Cycle) 849 639,000 I85 Yes 15 0 355 necticut) having a pH of about 9.0 maintained bythe appropriate addition of concentrated (28%) ammonium hydroxide.

The electroless nickel plated plaque samples were next electroplated bysubjecting the plaques to the sequential steps of the eleetroplatesequence set forth in the table below; the plaques were immersedsequentially into each treating bath of the composition identified inthe table below by immersing the plaques under the conditions also setforth in the table:

Electroplate Sequence Temperature Current Density, Time Plate ThicknessStep Bath Composition F. Amps/Sq. Ft. (Min.) In.

I 5% H,SO 70 until gas begins to evolve 2 Water Rinse 7O 025 3* NiStrike (Watts Ni) l35-I40 0-2 2-5 0.1 4 Water Rinse 70 0.2 5 5% H 0.2 6Water Rinse 70 0.2 7 MacDermid Bright Acid Copper 70 40 I5 0.5 8 WaterRinse 70 0.2 9 5% H SO 1% HCI 70 02 l0 Water Rinse 70 0.2 l l MacDermidBright Nickel Process No. 30 I40 40 5 0.1 12 Water Rinse 70 0.2

I3 5% H SO 70 0.2 14 Water Rinse 70 0,2 l5 MAC Chrome I I5 I25 20.02-0.06

The nickel-strike was deposited by immersing the plaque samples into theWatts type nickel plating bath operating at a current density of aboutl5 amps/sq. ft. for up to about 2 minutes after which the currentdensity of the hath was l'fliSLftl to about 30 amps/sq. ft.

ing of pyridine and up to about by volume of water before etching thesurface of said article.

2. Shaped articles of polyloxymethylene whenever prepared according tothe process of claim 1.

1. In a process for electroplating a shaped article of polyoxymethyleneby the sequential steps of etching the surface of said article with anacid etchant, neutralizing the etched surface of said article with abase solution, treating said article with a catalyst for electrolessdeposition, depositing by electroless plating a metal coating on saidarticle, and depositing by electroplating a metal coating on saidarticle, the improvement which comprises contacting said article with aliquid consisting of pyridine and up to about 75% by volume of waterbefore etching the surface of said article.
 2. Shaped articles ofpolyoxymethylene whenever prepared according to the process of claim 1.